Vector Magnetometry Localization of Subsurface Liquids

ABSTRACT

Systems and methods for locating a subsurface liquid can include an excitation coil configured to induce a magnetic resonance in a subsurface liquid, an array of magnetometers associated with the excitation coil configured to detect a magnetic vector of the magnetic resonance excited subsurface liquid, and a controller in communication with the array of magnetometers and configured to locate the subsurface liquid based on magnetic signals output from the array of magnetometers.

FIELD

The present disclosure generally relates to magnetometers, and more particularly, to magneto-optical defect magnetometers, such as diamond nitrogen vacancy magnetometers.

BACKGROUND

A number of industrial applications, as well as scientific areas such as physics and chemistry can benefit from magnetic detection and imaging with a device that has extraordinary sensitivity, ability to capture signals that fluctuate very rapidly (bandwidth) all with a substantive package that is extraordinarily small in size, efficient in power and infinitesimal in volume.

Atomic-sized magneto-optical defect centers, such as nitrogen-vacancy (NV) centers in diamond lattices, have excellent sensitivity for magnetic field measurement and enable fabrication of small magnetic sensors that can readily replace existing-technology (e.g., Hall-effect) systems and devices. Magneto-optical defect center materials include but are not be limited to diamonds, Silicon Carbide (SiC), Phosphorous, and other materials with nitrogen, boron, carbon, silicon, or other defect centers. The diamond nitrogen vacancy (DNV) sensors are maintained in room temperature and atmospheric pressure and can be even used in liquid environments. A green optical source (e.g., a micro-LED) can optically excite NV centers of the DNV sensor and cause emission of fluorescence radiation (e.g., red light) under off-resonant optical excitation. A magnetic field generated, for example, by a microwave coil can probe triplet spin states (e.g., with ms=−1, 0, +1) of the NV centers to split proportional to an external magnetic field projected along the NV axis, resulting in two spin resonance frequencies. The distance between the two spin resonance frequencies is a measure of the strength of the external magnetic field. A photo detector can measure the fluorescence (red light) emitted by the optically excited NV centers.

SUMMARY

Methods and systems are described for, among other things, a diamond nitrogen vacancy magnetometer.

Some embodiments relate to a system for locating a subsurface liquid. The system includes an excitation coil configured to induce a magnetic resonance in a subsurface liquid, an array of magnetometers associated with the excitation coil and configured to detect a magnetic vector of the magnetic resonance excited subsurface liquid, and a controller in communication with the array of magnetometers and configured to locate the subsurface liquid based on magnetic signals output from the array of magnetometers.

In some implementations, the array of magnetometers is an array of DNV magnetometers. In some implementations, the array of magnetometers is an array of SQUIDs. In some implementations, the excitation coil is a proton spin resonance excitation coil. In some implementations, the excitation coil and the array of magnetometers are mounted to a substructure. In some implementations, the controller is configured to deactivate the array of magnetometers during adiabatic passage preparation of the magnetic resonance signal. In some implementations, deactivating the array of magnetometers comprises deactivating an optical excitation source. In some implementations, deactivating the array of magnetometers comprises deactivating a RF excitation source. In some implementations, deactivating the array of magnetometers comprises deactivating an optical excitation source and a RF excitation source. In some implementations, the controller is configured to record an oscillatory proton (¹H) magnetic resonance (MR) Larmor precession in Earth's field by the array of magnetometers. In some implementations, the controller is configured to filter a local Earth field from a magnetic signal detected by the array of magnetometers. In some implementations, the filtering comprises periodic filtering (“AC”) pulse sequence operation of the magnetometers. In some implementations, the filtering comprises reversal of ¹H magnetization in alternating signal co-additions. In some implementations, locating the subsurface liquid includes the controller generating a numerical location of the subsurface liquid. In some implementations, locating the subsurface liquid includes the controller generating a two-dimensional reconstruction of the subsurface liquid. In some implementations, locating the subsurface liquid includes the controller generating a three-dimensional reconstruction of the subsurface liquid. In some implementations, the subsurface liquid is oil. In some implementations, the subsurface liquid is water.

Another implementation relates to a method for locating a subsurface liquid. The method includes activating a proton spin resonance excitation coil, activating an array of magnetometers, recording an oscillatory ¹H MR precession in Earth's field by the array of magnetometers, and generating a location of the subsurface liquid based on the recorded oscillatory ¹H MR precession.

In some implementations, the array of magnetometers is an array of DNV magnetometers. In some implementations, the array of magnetometers is an array of SQUIDs. In some implementations, the proton spin resonance excitation coil and the array of magnetometers are mounted to a substructure. In some implementations, the method further includes deactivating the array of magnetometers during adiabatic passage preparation. In some implementations, deactivating the array of magnetometers comprises deactivating an optical excitation source. In some implementations, deactivating the array of magnetometers comprises deactivating a RF excitation source. In some implementations, deactivating the array of magnetometers comprises deactivating an optical excitation source and a RF excitation source. In some implementations, the method further includes filtering a local Earth field from a magnetic signal detected by the array of magnetometers. In some implementations, the filtering includes AC filtering pulse sequence. In some implementations, the filtering includes reversal of ¹H magnetization in alternating signal co-additions. In some implementations, generating a location of the subsurface liquid includes generating a numerical location of the subsurface liquid. In some implementations, generating a location of the subsurface liquid includes generating a two-dimensional reconstruction of the subsurface liquid. In some implementations, generating a location of the subsurface liquid includes generating a three-dimensional reconstruction of the subsurface liquid. In some implementations, the subsurface liquid is oil. In some implementations, the subsurface liquid is water.

A further implementation relates to an apparatus. The apparatus includes a substructure, a proton spin resonance excitation coil mounted to the substructure and configured to induce a magnetic resonance in a subsurface liquid, an array of DNV magnetometers mounted to the substructure and configured to detect a magnetic vector of the magnetic resonance excited subsurface liquid, and a controller in communication with the array of magnetometers. The controller is configured to record an oscillatory ¹H MR precession in Earth's field by the array of magnetometers and locate the subsurface liquid based on magnetic signals output from the array of magnetometers.

In some implementations, the controller is configured to deactivate the array of DNV magnetometers during adiabatic passage preparation. In some implementations, deactivating the array of magnetometers comprises deactivating an optical excitation source. In some implementations, deactivating the array of magnetometers comprises deactivating a RF excitation source. In some implementations, deactivating the array of magnetometers comprises deactivating an optical excitation source and a RF excitation source. In some implementations, the controller is further configured to filter a local Earth field from a magnetic signal detected by the array of magnetometers. In some implementations, the filtering comprises AC filtering pulse sequence. In some implementations, the filtering comprises reversal of ¹H magnetization in alternating signal co-additions. In some implementations locating the subsurface liquid includes the controller generating a numerical location of the subsurface liquid. In some implementations, locating the subsurface liquid includes the controller generating a two-dimensional reconstruction of the subsurface liquid. In some implementations, locating the subsurface liquid includes the controller generating a three-dimensional reconstruction of the subsurface liquid. In some implementations, the subsurface liquid is oil. In some implementations, the subsurface liquid is water.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims, in which:

FIG. 1 illustrates an orientation of an NV center in a diamond lattice;

FIG. 2 illustrates an energy level diagram showing energy levels of spin states for the NV center;

FIG. 3 illustrates a schematic diagram of a NV center magnetic sensor system;

FIG. 4 is a graph illustrating the fluorescence as a function of an applied RF frequency of an NV center along a given direction for a zero magnetic field, and also for a non-zero magnetic field having a component along the NV axis;

FIG. 5 is a graph illustrating the fluorescence as a function of an applied RF frequency for four different NV center orientations for a non-zero magnetic field;

FIG. 6 is an illustrative overview of a system for localization of a subsurface liquid using a proton spin resonance excitation coil for inducing a magnetization in the subsurface liquid and an array of vector magnetometers to detect the location of the subsurface liquid;

FIG. 7 is an illustrative overview of sets of magnetometers of FIG. 6 outputting detection signals from the magnetized subsurface liquid;

FIG. 8 is an illustrative view depicting the detected location of the subsurface liquid based on the detection signals from the sets of magnetometers of FIG. 7; and

FIG. 9 is a process diagram for an illustrative process for detecting the location of the subsurface liquid using the array of magnetometers.

It will be recognized that some or all of the figures are schematic representations for purposes of illustration. The figures are provided for the purpose of illustrating one or more embodiments with the explicit understanding that they will not be used to limit the scope or the meaning of the claims.

DETAILED DESCRIPTION

In some aspects, methods and systems are disclosed for detecting the location of a subsurface liquid using an array of magnetometers. In some instances, the magnetometers may include diamond nitrogen-vacancy magnetometers.

Nitrogen-vacancy centers (NV centers) are defects in a diamond's crystal structure, which can purposefully be manufactured in synthetic diamonds as shown in FIG. 1. In general, when excited by green light and microwave radiation, the NV centers cause the diamond to generate red light. When excited with green light, the NV centers generate red light fluorescence. After sufficient time (on order of nanoseconds to microseconds) the fluorescence counts stabilize. When microwave radiation is added, the NV electron spin states are changed, and this results in a change in intensity of the red fluorescence. The changes in fluorescence are recorded as a measure of electron spin resonance. This technique is known as “optically detected magnetic resonance” or ODMR. By measuring the changes, the NV centers can be used to accurately detect the magnetic field strength.

The NV center may exist in a neutral charge state or a negative charge state. Conventionally, the neutral charge state uses the nomenclature NV⁰, while the negative charge state uses the nomenclature NV, which is adopted in this description.

The NV center has a number of electrons, including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

The NV center has rotational symmetry and, as shown in FIG. 2, has a ground state, which is a spin triplet with ³A₂ symmetry with one spin state m_(s)=0, and two further spin states m_(s)=+1, and m_(s)=−1. In the absence of an external magnetic field, the m_(s)=±1 energy levels are offset from the m_(s)=0 due to spin-spin interactions, and the m_(s)=±1 energy levels are degenerate, i.e., they have the same energy. The m_(s)=0 spin state energy level is split from the m_(s)=±1 energy levels by an energy of approximately 2.87 GHz for a zero external magnetic field.

Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the m_(s)=±1 energy levels, splitting the energy levels m_(s)=±1 by an amount 2 gμ_(B)Bz, where g is the Lande g-factor, μ_(B) is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is a straightforward matter and will not affect the computational and logic steps in the systems and methods described below.

The NV center electronic structure further includes an excited triplet state ³E with corresponding m_(s)=0 and m_(s)=±1 spin states. The optical transitions between the ground state ³A₂ and the excited triplet ³E are predominantly spin conserving, meaning that the optical transitions are between initial and final states that have the same spin. For a direct transition between the excited triplet ³E and the ground state ³A₂, a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

There is, however, an alternative non-radiative decay route from the triplet ³E to the ground state ³A₂ via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the m_(s)=±1 spin states of the excited triplet ³E to the intermediate energy levels is significantly greater than the transition rate from the m_(s)=0 spin state of the excited triplet ³E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet ³A₂ predominantly decays to the m_(s)=0 spin state over the m_(s)=±1 spins states. These features of the decay from the excited triplet ³E state via the intermediate singlet states A, E to the ground state triplet ³A₂ allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the m_(s)=0 spin state of the ground state ³A₂. In this way, the population of the m_(s)=0 spin state of the ground state ³A₂ may be “reset” to a maximum polarization determined by the decay rates from the triplet ³E to the intermediate singlet states.

Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet ³E state is less for the m_(s)=±1 states than for the m_(s)=0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the m_(s)=±1 states of the excited triplet ³E state will decay via the non-radiative decay path. The lower fluorescence intensity for the m_(s)=±1 states than for the m_(s)=0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the m_(s)=±1 states increases relative to the m_(s)=0 spin, the overall fluorescence intensity will be reduced.

FIG. 3 is a schematic diagram illustrating a NV center magnetic sensor system 300 that uses fluorescence intensity to distinguish the m_(s)=±1 states, and to measure the magnetic field based on the energy difference between the m_(s)=+1 state and the m_(s)=−1 state, as manifested by the RF frequencies corresponding to each state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system further includes an RF excitation source 330, which provides RF radiation to the NV diamond material 320. Light from the NV diamond may be directed through an optical filter 350 to an optical detector 340.

The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330, when emitting RF radiation with a photon energy resonant with the transition energy between ground m_(s)=0 spin state and the m_(s)=+1 spin state, excites a transition between those spin states. For such a resonance, the spin state cycles between ground m_(s)=0 spin state and the m_(s)=+1 spin state, reducing the population in the m_(s)=0 spin state and reducing the overall fluorescence at resonances. Similarly, resonance and a subsequent decrease in fluorescence intensity occurs between the m_(s)=0 spin state and the m_(s)=−1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the m_(s)=0 spin state and the m_(s)=−1 spin state.

The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green (light having a wavelength such that the color is green), for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the m_(s)=0 spin state of the ground state ³A₂ to a maximum polarization, or other desired polarization.

For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range that includes the zero splitting (when the m_(s)=±1 spin states have the same energy) photon energy of approximately 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in FIG. 4 for different magnetic field components Bz along the NV axis, where the energy splitting between the m_(s)=−1 spin state and the m_(s)=+1 spin state increases with Bz. Thus, the component Bz may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples of pulsed excitation schemes include Ramsey pulse sequence (described in more detail below), and spin echo pulse sequence.

In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. FIG. 5 illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component Bz along each of the different orientations may be determined. These results, along with the known orientation of crystallographic planes of a diamond lattice, allow not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

While FIG. 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general, the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. Magneto-optical defect center materials include but are not be limited to diamonds, Silicon Carbide (SiC), Phosphorous, and other materials with nitrogen, boron, carbon, silicon, or other defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material.

FIG. 6 depicts an overview of a system 600 for localization of a subsurface liquid 690 using a proton spin resonance excitation coil 610 for inducing a magnetization in the subsurface liquid 690, an array 620 of vector magnetometers 622 to detect the location of the subsurface liquid 690, and a controller 650 for generating a location, two-dimensional reconstruction, and/or three-dimensional reconstruction of the subsurface liquid 690 based on the output of the array 620 of vector magnetometers 622. The subsurface liquid 690 may be a liquid of interest for the location, such as oil, other hydrocarbons, water, or other liquids. For instance, oil may be of interest in artic, Antarctic, tundra, and/or other locations where oil and water may be mixed. In particular, locating oil during an oil spill may be important for recovery and/or clean-up procedures. In certain locations, such as the arctic, Antarctic, and/or other ice or snow areas, visual location of the oil may be difficult as the oil may be below the surface, such as mixed in and/or below snow or ice, underground, in water under ice, etc. Moreover, site surveys can be expensive, dangerous, and/or ineffective for remote and/or difficult to reach areas. Accordingly, accurate locating of the oil may be useful to expedite recovery, containment, and/or clean-up efforts for spilled oil. In other instances, subsurface oil can be located for extraction purposes. In further instances, subsurface water can be located in arid or other geographic locations for extraction and use.

The proton spin resonance excitation coil 610 is a coil for inducing magnetic resonance in the subsurface liquid 690, such as oil, by generating a magnetic resonance (MR) field from the coil. The proton spin resonance excitation coil 610 may be a flat coil, such as a flat figure-8gradiometer coil such as that described in L. Chavez, et al., “Detecting Arctic oil spills with NMR: a feasibility study”, Near Surface Geophysics, Vol 13, No 4, August 2015, the disclosure of which is incorporated by reference in its entirety herein. The proton spin resonance excitation coil 610 is configured to induce magnetic ¹H magnetic resonance in the subsurface liquid 690 and any other different liquids below the position of the proton spin resonance excitation coil 610. By exploiting the magnetic relaxation differential between the subsurface liquid of interest and any other liquids near the subsurface liquid of interest, a general location of the subsurface liquid can be estimated. In some implementations, the proton spin resonance excitation coil 610 may be mounted to a substructure, such as a tubular frame, piping, or other substructure to maintain the coil 610 configuration and shape. In some instances, the substructure may be coupled to a vehicle, such as a helicopter, or other device to move the substructure and the proton spin resonance excitation coil 610. The proton spin resonance excitation coil 610 is a large scale coil, such as on the order of 10 meters, and may be difficult to detect a particular location of the subsurface liquid 690. Accordingly, an array 620 of magnetometers 622 may be implemented with the proton spin resonance excitation coil 610 to exploit the magnetic resonance excitation from the proton spin resonance excitation coil 610 and detected a location of the subsurface liquid 690 using the vector signals from sets of magnetometers 622.

The array 620 of the magnetometers 622 may be mounted to the substructure to which the proton spin resonance excitation coil 610 is mounted and/or may be independent of the proton spin resonance excitation coil 610. The array 620 is generally positioned in a circular arrangement relative to the proton spin resonance excitation coil 610, but the array 620 may have other geometric configurations, such as square, rectangular, triangular, ovular, etc. Other possible array configurations may include a two-dimensional array filling a circular area subtended by the excitation coil or a three-dimensional array positioned above or below the excitation coil with an area projected within the coil. The magnetometers 622 of the present disclosure are DNV magnetometers, but other vector magnetometry devices may be utilized as well, such as superconducting quantum interference devices (SQUIDs). Such SQUID devices are described in greater detail in L Q Qiu, et al,, “SQUID-detected NMR in Earth's Magnetic Field”, 8th European Conference on Applied Superconductivity (ELICAS 2007), Journal of Physics: Conference Series 97 (2008) 012026, IOP Publishing; A. N. Matlashov, et al., “SQUIDs for Magnetic Resonance Imaging at Ultra-low Magnetic Field”, PIERS online 5.5 (2009); and/or J. Clarke, et al., “SQUID-Detected Magnetic Resonance Imaging in Microtesla Fields”, Annual Review of Biomedical Engineering, Vol. 9: 389-413 (2007), the disclosures of which are incorporated by reference herein in their entirety. In some implementations, the array of magnetometers is an array of gas-cell detectors.

The controller 650 is electrically coupled to and/or in communication with the array 620 of magnetometers 622 and, in some implementations, the proton spin resonance excitation coil 610 to control the magnetometers 622 and, optionally, the proton spin resonance excitation coil 610. In addition, the controller 650 is configured to utilize the output from the magnetometers 622 to generate a location, two-dimensional reconstruction, and/or three-dimensional reconstruction of the subsurface liquid 690 as will be described in greater detail in reference to FIG. 9.

Referring to FIG. 7, once the proton spin resonance excitation coil 610 induces a magnetic resonance in the subsurface liquid 690, the array 620 of magnetometers 622 can be activated to detect the magnetic field vectors of the subsurface liquid 690. As shown in FIG. 7, sets 630, 632, 634, 636 of magnetometers 622 may be utilized to determine detected magnetic vectors, M, and magnetic intensity, IMI, for the magnetized subsurface liquid 690. The detected magnetic vectors and magnetic intensity can be determined by detecting the Earth's magnetic field at the location without the subsurface liquid 690 being magnetized and removing the result from the magnetic signal detected by the magnetometers 622 once the subsurface liquid 690 is magnetized by the proton spin resonance excitation coil 610. In other implementations, the magnetometers can be operated in a mode that filters out magnetic fields which are effectively static, such as the Earth's field, on the time scale of the magnetometer measurements (typically miliseconds). The magnetic intensity, IMI, is proportional to the distance of the subsurface liquid 690 relative to each magnetometer 622 and/or set of magnetometers 630, 632, 634, 636. In some implementations, a time-varying nuclear magnetic resonance, M(t), can be modeled as a radiating source, such as a dipole radiator. The magnetic vector, M, provides a direction of the subsurface liquid 690 relative to each magnetometer 622 and/or set of magnetometers 630, 632, 634, 636. Using the foregoing, a back-projection or other reconstruction algorithm can be implemented to locate the subsurface liquid 690, as shown in FIG. 8, from the magnetic vector and/or magnetic intensity measured by 1 through N magnetometers 622 and/or sets of magnetometers 622.

FIG. 9 depicts a process 700 for utilizing the proton spin resonance excitation coil 610 and array 620 of magnetometers 622 to detect the subsurface liquid 690. The process 700 may be implemented by controller 650 of FIG. 6. The process 700 includes deactivating or “blanking” the magnetometers (block 702). The deactivation or “blanking” may include deactivating an optical excitation source, such as optical excitation source 310 of FIG. 3, for a DNV magnetometer and/or deactivating a RF excitation source, such as RF excitation source 330 of FIG. 3. Deactivating the optical and/or RF excitation source occurs during the adiabatic passage preparation with the proton spin resonance excitation coil 610. Thus, the magnetometers 622 are not affected by the proton spin resonance excitation coil 610.

The process 700 further includes activating the proton spin resonance excitation coil 610 (block 704). Activating the proton spin resonance excitation coil 610 induces a magnetic resonance in the subsurface liquid 690 that will be measured by the magnetometers 622. The process 700 further includes activating the magnetometers 622 (block 706). For magnetometers such as DNV magnetometers, the activation step can be rapid after the proton spin resonance excitation coil 610 is deactivated. That is, the rapid “turn on” time for DNV magnetometers can be used to detect the magnetic signal from the magnetic resonant excited subsurface liquid 690 quickly after the excitation coil 610 is deactivated, allowing for a larger magnetic signal (and therefore a more easily discernable magnetic signal) to be detected than other magnetometers. The process 700 further includes recording the oscillatory ¹H MR precession in Earth's field by the magnetometers (block 708). The process 700 further includes filtering the local, approximately static, Earth field from the magnetic signal detected by the magnetometers (block 710). In some implementations, the filtering may discriminate the magnetic signal of the subsurface liquid 690 from the local Earth field by AC filtering pulse sequence, such as Hahn Echo. In other implementations, the filtering may use a reversal of ¹H magnetization in alternating signal co-additions to enhance discrimination of the magnetic signal of the subsurface liquid 690 relative to the local Earth field. The process 700 includes generating a location, a two-dimensional reconstruction, and/or a three-dimensional reconstruction of the subsurface liquid 690 based on the filtered magnetic signal from the magnetometers (block 712). The generation of the location (e.g., scalar or numerical location), two-dimensional reconstruction, and/or three-dimensional reconstruction may be through a back-projection and/or tomographic algorithm for image reconstruction, such as those similar to magnetic resonance imaging (MRI) and/or computed tomography (CT).

The foregoing description is provided to enable a person skilled in the art to practice the various configurations described herein. While the subject technology has been particularly described with reference to the various figures and configurations, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the subject technology.

While the above discussion primarily refers to circuits and/or circuitry, the circuits may include a microprocessor or multi-core processors that execute software, one or more implementations are performed by one or more integrated circuits, such as application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs). In one or more implementations, such integrated circuits execute instructions that are stored on the circuit itself.

The description of the subject technology is provided to enable any person skilled in the art to practice the various embodiments described herein. While the subject technology has been particularly described with reference to the various figures and embodiments, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the subject technology.

There may be many other ways to implement the subject technology. Various functions and elements described herein may be partitioned differently from those shown without departing from the scope of the subject technology. Various modifications to these embodiments may be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other embodiments. Thus, many changes and modifications may be made to the subject technology, by one having ordinary skill in the art, without departing from the scope of the subject technology.

A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. All structural and functional equivalents to the elements of the various embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description. 

What is claimed is:
 1. An apparatus comprising: a substructure; a proton spin resonance excitation coil mounted to the substructure and configured to induce a magnetic resonance in a subsurface liquid; an array of DNV magnetometers mounted to the substructure and configured to detect a magnetic vector of the magnetic resonance excited subsurface liquid; and a controller in communication with the array of magnetometers and configured to: record an oscillatory proton (¹H) magnetic resonance (MR) Larmor precession in Earth's field by the array of magnetometers, and locate the subsurface liquid based on magnetic signals output from the array of magnetometers.
 2. The apparatus of claim 1, wherein the controller is configured to deactivate the array of DNV magnetometers during adiabatic passage preparation of a magnetic resonance signal of the proton spin resonance excitation coil.
 3. The apparatus of claim 2, wherein deactivating the array of magnetometers comprises deactivating an optical excitation source.
 4. The apparatus of claim 2, wherein deactivating the array of magnetometers comprises deactivating a RF excitation source.
 5. The apparatus of claim 2, wherein deactivating the array of magnetometers comprises deactivating an optical excitation source and a RF excitation source.
 6. The apparatus of claim 1, wherein the controller is further configured to filter a local Earth field from a magnetic signal detected by the array of magnetometers.
 7. The apparatus of claim 6, wherein the filtering comprises periodic filtering (“AC”) pulse sequence operation of the array of DNV magnetometers.
 8. The apparatus of claim 6, wherein the filtering comprises reversal of ¹H magnetization in alternating signal co-additions.
 9. The apparatus of claim 6, wherein locating the subsurface liquid includes the controller generating a numerical location of the subsurface liquid.
 10. The apparatus of claim 6, wherein locating the subsurface liquid includes the controller generating a two-dimensional reconstruction of the subsurface liquid.
 11. The apparatus of claim 6, wherein locating the subsurface liquid includes the controller generating a three-dimensional reconstruction of the subsurface liquid.
 12. The apparatus of claim 1, wherein the subsurface liquid is oil.
 13. The apparatus of claim 1, wherein the subsurface liquid is water.
 14. A system for locating a subsurface liquid, the system comprising: an excitation coil configured to induce a magnetic resonance in a subsurface liquid; an array of magnetometers associated with the excitation coil, the array of magnetometers configured to detect a magnetic vector of the magnetic resonance excited subsurface liquid; and a controller in communication with the array of magnetometers and configured to locate the subsurface liquid based on magnetic signals output from the array of magnetometers.
 15. The system of claim 14, wherein the array of magnetometers is an array of DNV magnetometers.
 16. The system of claim 14, wherein the array of magnetometers is an array of SQUIDs.
 17. The system of claim 14, wherein the excitation coil is a proton spin resonance excitation coil.
 18. The system of claim 14, wherein the excitation coil and the array of magnetometers are mounted to a substructure.
 19. The system of claim 14, wherein the controller is configured to deactivate the array of magnetometers during adiabatic passage preparation of a magnetic resonance signal of the excitation coil.
 20. The system of claim 19, wherein deactivating the array of magnetometers comprises deactivating an optical excitation source.
 21. The system of claim 19, wherein deactivating the array of magnetometers comprises deactivating a RF excitation source.
 22. The system of claim 19, wherein deactivating the array of magnetometers comprises deactivating an optical excitation source and a RF excitation source.
 23. The system of claim 14, wherein the controller is configured to record an oscillatory proton (¹H) magnetic resonance (MR) Larmor precession in Earth's field by the array of magnetometers.
 24. The system of claim 23, wherein the controller is configured to filter a local Earth field from a magnetic signal detected by the array of magnetometers.
 25. The system of claim 24, wherein the filtering comprises periodic filtering (“AC”) pulse sequence operation of the array of magnetometers.
 26. The system of claim 24, wherein the filtering comprises reversal of ¹H magnetization in alternating signal co-additions.
 27. The system of claim 14, wherein locating the subsurface liquid includes the controller generating a numerical location of the subsurface liquid.
 28. The system of claim 14, wherein locating the subsurface liquid includes the controller generating a two-dimensional reconstruction of the subsurface liquid.
 29. The system of claim 14, wherein locating the subsurface liquid includes the controller generating a three-dimensional reconstruction of the subsurface liquid.
 30. The system of claim 14, wherein the subsurface liquid is oil.
 31. The system of claim 14, wherein the subsurface liquid is water.
 32. A method for locating a subsurface liquid comprising: activating a proton spin resonance excitation coil; activating an array of magnetometers; recording an oscillatory proton (¹H) magnetic resonance (MR) Larmor precession in Earth's field by the array of magnetometers; and generating a location of the subsurface liquid based on the recorded oscillatory proton (¹H) magnetic resonance (MR) Larmor precession.
 33. The method of claim 32, wherein the array of magnetometers is an array of DNV magnetometers.
 34. The method of claim 32, wherein the array of magnetometers is an array of SQUIDs.
 35. The method of claim 32, wherein the proton spin resonance excitation coil and the array of magnetometers are mounted to a substructure.
 36. The method of claim 32 further comprising deactivating the array of magnetometers during adiabatic passage preparation of a magnetic resonance signal of the proton spin resonance excitation coil.
 37. The method of claim 36, wherein deactivating the array of magnetometers comprises deactivating an optical excitation source.
 38. The method of claim 36, wherein deactivating the array of magnetometers comprises deactivating a RF excitation source.
 39. The method of claim 36, wherein deactivating the array of magnetometers comprises deactivating an optical excitation source and a RF excitation source.
 40. The method of claim 32 further comprising filtering a local Earth field from a magnetic signal detected by the array of magnetometers.
 41. The method of claim 40, wherein the filtering comprises periodic filtering (“AC”) pulse sequence operation of the array of magnetometers.
 42. The method of claim 40, wherein the filtering comprises reversal of ¹H magnetization in alternating signal co-additions.
 43. The method of claim 32, wherein generating a location of the subsurface liquid includes generating a numerical location of the subsurface liquid.
 44. The method of claim 32, wherein generating a location of the subsurface liquid includes generating a two-dimensional reconstruction of the subsurface liquid.
 45. The method of claim 32, wherein generating a location of the subsurface liquid includes generating a three-dimensional reconstruction of the subsurface liquid.
 46. The method of claim 32, wherein the subsurface liquid is oil.
 47. The method of claim 32, wherein the subsurface liquid is water. 